Wet smelting method for nickel oxide ore

Abstract

A wet smelting method for nickel oxide ores from which nickel, cobalt, etc. are recovered is provided with which it is possible to reduce the consumption of an acid in leaching, such as sulfuric acid, and to recover valuable metals. The method comprises: step (A) in which nickel oxide ores as a raw material are separated into a limonite-type ore having a low magnesium content and a saprolite-type ore having a high magnesium content; step (B) in which the saprolite-type ore is subjected to normal-pressure leaching under given standardized leaching conditions using the pressure leachate obtained by pressure leaching in step (C); and step (C) in which the limonite-type ore obtained in step (A) is mixed with the normal-pressure leaching residue obtained in step (B) and the mixture is reacted with sulfuric acid in an acidic atmosphere having a high temperature and a high pressure, thereby conducting pressure leaching.

The invention claimed is: 
     
       1. A wet smelting method for nickel oxide ore by which valuable metals are recovered from the nickel oxide ore, the method comprising:
 a step A of separating the nickel oxide ore into a limonite ore having a low magnesium grade with a magnesium grade of 2% by weight or less and a saprolite ore having a high magnesium grade with a magnesium grade of more than 2% by weight; 
 a step B of normal-pressure leaching the saprolite ore obtained in the step A by adding a pressure leachate which is obtained by pressure leaching in a step C described below and in which the concentration of sulfuric acid is adjusted such that the value, which is obtained by dividing the total value of the concentration of free acid contained in the pressure leachate and the concentration of iron ions calculated on the assumption that the existence form is trivalent by the grade of magnesium contained in the saprolite ore, becomes 1.5 mol/mol equivalent or less, to obtain a normal-pressure leachate and a normal-pressure leaching residue; and 
 a step C of performing pressure leaching by mixing the limonite ore obtained in the step A and the normal-pressure leaching residue obtained in the step B and then reacting the resultant mixture with sulfuric acid in an acidic atmosphere under high temperature and high pressure, to obtain a pressure leachate.